Micro-photometry



Jan. 28, T958 G. c. F. BLET 2,821,103

MICRO-PHOTOMETRY Filed oct. 27, 195s fw S 59/ H IS AT TORN EYS UnitedStates Patent O MICRO-pHoroMETRY Georges Charles Frdric Blet, Paris,France, assignor to Centre National de la Recherche Scientifique, Paris,France, a corporation of France Application October 27, 1953, Serial No.388,627

Claims priority, application France October 30, 1952 Claims. (Cl. 88-14)lt is often necessary to plot the microphotometric curve for a variabledensity coating, such as a photographic paper positive or achromatographic recording, for example, or to check the condition of asurface or the authenticity of a document of some kind.

Micro-photographic devices are known, comprising a light source and aphoto-electric cell placed on either side of the document, the lightpassing therethrough. To make the document translucent, it is dippedinto a fatty substance, which action in most cases results in adestruction of thel document; the analysis has a very reduced finenesswhich is limited by more or less pronounced faults in the texture of thesupport.

Devices are also known using photo-electric cells receiving the lightdiffused by the document to be examined, which offer, in particular, amuch attenuated sensitivity due to the low intensity of the diffusedlight and to the inertia inherent to the cells.

An object of the present invention is to obviate these various drawbacksand, especially, to allow, in a very simple manner, themicro-photometric analysis by direct readings, or by continuous ordiscontinuous recordings, of all documents, without any alteration ordestruction of said documents, The invention concerns a microphotometryprocess consisting in picking up and distributing in a homogeneousmanner almost all the light diffused by the document, which then acts ona sensitive receiving element.

The invention also concerns a device for the application of thisprocess.

According to the process of the invention, through an integrating sphereprovided with an analysis Slot, possibly adjustable and placed as closeas possible to the document to be examined, a region-image of a lightsource is formed onto the document, by means of an optical system, whichimage acts as a secondary light source, whereby the incident rays arereilected on themselves, and almost all the light diffused by thedocument enters, through the analysis slot, the integrating sphere,inside which the lighting is uniform and inside which, after undergoingmultiple diffusions, it acts on a sensitive receiving element, arrangedat any point in the sphere and connected with a measuring or recordingdevice, after an amplification of the current if necessary.

Using an integrating sphere, inside which the lighting is uniform andplacing it almost tangentially to the document, makes it possible topick up almost all of the light diffused by the illuminated area, whichthus acts in its entirety on the sensitive receiving element, regardlessof its position inside the integrating sphere.

The integrating sphere may be made of any suitable metal, copper, ironsheet, aluminum, etc.; its inner surface is made so as to have a maximumdiffusion power; this result is obtained by any suitable means. Theinner surface may, for instance, be coated with a layer of magnesia, orwith a matt coating with a base of white cellulose paint, or anydiffusion coating adhering suitably "ice to the material constitutingthe sphere, or again, it may be subjected to an anodic surface treatmentor a treatment similar to parkerizing.

As the optical system makes it possible to form an image of the lightsource on the document to be examined and transforms the latter into asecondary light source of which the surface diffused light alone ispicked up, there becomes possible to examine all documents with nonecessity of making them translucent, by any preliminary dipping intofatty substances or otherwise; thus, the action of the latter on thedocument and support being eliminated, remarkable results are obtained,both as regards the sharpness of curves, for instance and the finenessof analysis, the document, finally remaining unchanged, the influence ofthe support structure being eliminated.

The invention makes it possible, finally, by the use of light filtersand sensitive receiving elements, to carry out a microphotometricanalysis at all wave lengths, thus making its utilization particularlyvaluable for chromatography.

When eltecting a continuous recording of the variations caused by thesurface of a document, and transmitted by the photoelectric cell, it isconvenient to adjust the unwinding of the recording film to a speedwhich is a known multiple of the speed of displacement of the documentin front of the analysis slot of the integrating sphere. This makes itpossible to determine rapidly and without any risk of error, theinteresting points on the document, from a simple reading and comparisonof the recording.

For a better understanding of the invention and of various additionaldetails, advantages and characteristics thereof, reference is made tothe following description of an embodiment thereof taken in conjunctionwith the accompanying drawings wherein:

Figure l is a side elevation in the from of a diagrammatic cross sectiontaken along the axis of the said embodiment;

Figure 2 is a view, taken as indicated by the arrows 2A-2A, of certaindetails of the embodiment of Figure l; and

Figure 3 is a view in perspective of the embodiment of Figure l.

The device comprises essentially a light source 1, consisting, forexample, of a lamp having a rectilinear lament, placed inside a lightbox2, a passage 5 connecting the light box 2 with the integrating sphere 7;the passage 5 is provided with a slot 4 illustrated in Figure l as ablock. This slot 4 has a section adjustable by any suitable means, forexample, of the type generally used for the entrance slots ofspectrographs. Usually the section of the entrance slot of aspectrograph is adjustable in length and width. The length and width ofthe slot section of a spectrograph may be symmetrically controlled bytwo devices of which the first thereof (Figure 2) is comprised of ascrew 21 with two different pitches 23 and 24 respectively driving twonuts 25, 26 closer to or apart from each other when an adjusting knob 22for the screw is turned in opposite directions. The nuts 2S, 26 carryshields 27, 28 which define slot S and make it narrower or wider in afirst dimension. A second similar device (not shown) lies across axis XYin perpendif' -is metallic, for instance, and coated inside with adiffusing material such as magnesia, comprises the sensitive receivingelement 10, consisting of a sensitive photo-electric cell and ananalysis slot 8, arranged as close as possible and lparallel to thedocument to be examined. This arrangement of the sphere 7 and slot 8 issuch that, practically, all of the diffused light be picked up by theslot 8, i. e. that the solid angle be substantially equal to 2.

The dimensions of the slot 4 are preferably about ten to ltwelve timessmaller than those of the slot 8.

The document to be examined, 9, is placed on a conventional deviceallowing an examination of all areas. This device may take the form, forexample, of two drums 12 and 13 of which the former is mounted on alshaft 16 and the latter on a shaft 17. The document 9 to be analyzed isfastened in a loop around these drums to be moved thereby past theanalysis sloty 8 as the shaft 16 is driven by a motor (not shown).

Within the scope of the invention, the adjustable slot 4 and theanalysis slot 8 may be replaced by diaphragms or any other conventionaldevice having the same function.

The sensitive receiving element 10 may consist of any sensitivephoto-electric cell, the current generated being amplified if necessary.Thus the output of the photoelectric cell may be amplified by anamplifier interposed between the photoelectric cell and a registeringdevice 21. This registering device may be a conventional indicatinggalvanometer. If a record is desired, the galvanometer 21 may beprovided with a recording pen (not shown) adapted to inscribe a trace ona. recording medium as, say, a registering band 30 fastened in a looparound the drums 14 and 15, these drums being respectively mounted onthe shafts 16, 17. With the registering band so arranged, the band willmove past galvanometer 21 at the same speed as the movement of document9 past analysis slot 8, the displacement of the hand in recording thusbeing a known multiple of displacement of the document in front of theanalysis slot.

It is possible to simplify the optical arrangement, which forms theimage of the light source on the document to be examined, by omittingthe convergent system 3 and suitably adjusting the diaphragm or slot 4so that the image be formed on the document.

In case it is desired to carry out an analysis for a predeterminedregion of the spectrum, suitable colour filters are interposed at 11. Asa means for interposing separate color filters, there may be provided adisk 18 perforated with holes bearing filters F, the disk beingrotatable around a shaft 19. Such a disk may be provided with one holedeprived of a filter, so as to cause the beam to pass directly to thedocument. The filters may be colored in case a colored document isstudied. For instance, when a more or less colored blue band is to hestudied, filters may be used of a complementary orange color in order toenhance the sensitivity.

It must be stated that the document can be either a printed or coatedpaper, or any surface material coated or not, various portions of whichcan be disposed parallel and close to the analysis slot.

What I claim is:

1. An apparatus for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a first slot paralleland as close as possible to the surface, a light sensitive receiverfixed on the inside wall of said spherical part, at the other end of thecasing and inside thereof a source of light centered on the axis of thecasing, an adjustable slot uniformly illuminated by the source of lightperpendicular to the axis of the casing between the source 'of'light'andthe spherical part of the casing, an optical device between the slot andthe surface for concentrating the images of said adjustable slot on thesurface through the first slot, and a measuring device connected to thelight sensitive receiver.

2. An apparatus for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a first slot paralleland as close as possible to the surface, a light sensitive receiverfixed on the inside wall of said spherical part, at the other end of thecasing and inside thereof a source of light centered on the axis of thecasing, an adjustable slot uniformly illuminated by the source of lightperpendicular to the axis of the casing between the source of light andthe spherical part of the casing, an optical device between the slot andthe surface for concentrating the images of said adjustable slot on thesurface through the first slot, and a registering device connected tothe light sensitive receiver.

3. An apparatus for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a` first slot paralleland as close as possible to the surface, a light sensitive receiverfixed on the inside wall of said spherical part, at the other end of thecasing and inside thereof a source of light centered on the axis of thecasing, an adjustable slot uniformly illuminated by the source of lightperpendicular to the axis of the casing between the source of light andthe spherical part of the casing, an optical device between the slot andthe surface for-concentrating the images of said adjustable slot on thesurface through the first slot, a measuring device connected to thelight sensitive receivers, and a registering device connected to themeasuring device.

4. An apparatus for surveying the conditions of surface of bodiescapabley of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of'the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a first slot pai'- alleland as close as possible to the surface, a light sensitive' receiverfixed on the inside wall of said spherical part, at the other end of thecasing and inside thereof centered on the axis of the casing, a firstoptical device perpendicular to the axis, an adjustable slot uniformlyilluminated through the first optical device perpendicular to the axisbetween the first optical device and the spherical part of the casingand constituting a secondary source of. light, a second optical devicebetween the slot and the surface for concentrating the images of saidadjustable slot o n the surface through the first slot, and a measuringdevice connected to the light sensitive receiver.

5. An apparatus-for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a first slot paralleland as close as possible to the surface, a light sensitive receiverfixed on the inside wall of said spherical part, at the other end of thecasing and inside thereof a source of light centered on the yaxis of thecasing, a first optical device perpendicular to the axis, an adjustableslot uniformally illuminated through the first optical deviceperpendicular to the axis between the first optical device and thespherical part of the casing and constituting a secondary source oflight, a second optical device between the slot and the surface forconcentrating the images of said adjustable slot on the surface throughthe first slot, and a registering device connected to the lightsensitive receiver.

6. An apparatus for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a first slot paralleland as close as possible to the surface, a light sensitive receiverfixed on the inside wall of said spherical part, at the other end of thecasing and inside thereof a source of light centered on the axis of thecasing, an adjustable slot uniformly illuminated by the source of lightperpendicular to the axis of the casing between the source of light andthe `spherical part of the casing, a chromatic filter perpendicular tothe axis of the casing, an optical device between the filter and thesurface for concentrating the image of said adjustable slot on thesurface through the first slot, and a measuring device connected to thelight sensitive receiver.

7. An apparatus for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a first slot paralleland as close as possible to the surface, a light sensitive receiver xedon the inside wall of said spherical part, -at the other end of thecasing and inside thereof a source of light centered on the axis of thecasing, an adjustable slot uniformly illuminated by the source of lightperpendicular to the axis of the casing between the source of light andthe spherical part of the casing, a chromatic filter perpendicular tothe axis of the casing, an optical device between the filter and thesurface for concentrating the image of said adjustable slot on thesurface through the first slot, and a registering device connected tothe light sensitive receiver.

8. An apparatus for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a first slot paralleland as close as possible to the surface, a photo-electric cell fixed onthe inside wall of said spherical part, at the other end of the casingand inside thereof a source of light centered on the axis of the casing,an adjustable slot uniformly illuminated by the source of lightperpendicular to the axis of the casing between the source of light andthe spherical part of the casing, an optical device between the slot andthe surface for concentrating the image of said adjustable slot on thesurface through the first slot and a measuring device connected to thephoto-electric cell.

9. An apparatus for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical casing having itsaxis perpendicular to said surface, the end of the casing which istowards said surface being substantially fully spherical and having aninner diffusing surface, in said spherical part a first slot paralleland as close as possible to the surface, a light sensitive receiverfixed on the inside wall of said spherical part, at the other end of thecasing and inside thereof a source of light centered on the axis of thecasing, an adjustable slot uniformly illuminated by the source of lightperpendicular to the axis of the casing between the source of light andthe spherical part of the casing, an optical device between the slot andthe surface for concentrating the image of said adjustable slot on thesurface through the first slot, a registering device connected to thelight sensitive receiver, and means for moving in synchronism thesurface and the registering device.

10. An apparatus for surveying the conditions of surface of bodiescapable of diffusing light, comprising a symmetrical metallic casinghaving its axis perpendicular to said surface, the end of said casingwhich is towards said surface being substantially fully spherical andbearing on its inside wall a diffusing coating, in said spherical part afirst slot parallel and as close as possible to the surface, a lightsensitive receiver fixed on the inside wall of said spherical part, atthe other end of the casing and inside thereof a source of lightcentered on the axis of the casing, an adjustable slot uniformlyilluminated by the source of light perpendicular to the axis of thecasing between the source of light and the spherical part of the casing,an optical device between the slot and the surface for concentrating theimage of said adjustable slot on the surface through the first slot, anda measuring device connected to the light sensitive receiver.

References Cited in the le of this patent UNITED STATES PATENTS Tuttleet al Feb. 16, 1943 Schurcliff Apr. 18, 1944 OTHER REFERENCES

